Heat exchanger



Nov. 12, 1935. C LUCKE 2,021,117

HEAT EXCHANGER Filed March 21, 1931 2 Sheets-Sheet 1 Fig f 1 INVENTORATTORNEY Charles E Z ucke Nov. 12, 1935. c. E. LucKE 2,021,117

HEAT EXCHANGER Filed March 21, 1931 2 Sheets-Sheet 2 Upward Defleclianunk" IIH 9, a;

' INVENTOR Charles E. Luoke ATTORNEY heat exchange. apparatus.

I tube, and in the opposite direction on'the op- V have. advantagesPatented Nov. 12, 1935 UNITED STATES 2,021,117 I HEAT EXCHANGER CharlesE. Lucke,

The Babcock &

New York, N. Y., assignor to Wilcox Company, Bayonne,

N. J., a corporation of New Jersey Application March 21, 1931, SerialNo. 524,252 12 Claims. (01. 251-230) This invention relates toimprovements in fluid Specifically "it presents an arrangement ofhelically finned tubes, as an improvement in fluid heat transferapparatus' An object is to render more effective and complete theheatexchange from one fluid to an-' other.

The invention is also intended to reduce heat losses resulting fromineffective and incomplete scouring action along fluid containing tubesreceiving heat from passing gases.

A further object isto promote economy of cost of installation and thecompactness of fluid heat exchangers. I

The invention is set forth with particular reference, to theaccompanying drawings, in which:

Fig. 1 is a sectional view indicating a part of a return bend economizerhaving adjacent fluid conducting tubes formed with oppositely projectingfins, which are interlocked.

Fig. 2 is a detailed view of a section of one of the finned tubes of aheat exchange apparatus such as that shown in Fig. 1.

Fig. 3 is a detailed view of sections of adjoining finned tubes withoppositely directed interlocked fins.

Fig. 4: is a diagrammatic view with legends in dicating the action ofgases upon finned tubes having a. pitch greater than their criticalpitch.

Fig. 5 is a fragmentary view showing adjoining fluid heat exchange tubeswith fins arranged as right hand and left hand helices and practi-'.cally completely overlapped.

v Fig. 6 is a fragmentary sectional view indicating finned sectionswhich may be formed by making radial saw 1; ts in the illustrative fins.

The passage of astream of gas transversely of a helically finned tuberesults in a deflection of the gas in one direction on one side of theposite side of the tube.. Thedeflection of the gas is inopposite to thecharacteristics of the helices. Such tubes transfer apparatus but theycannot be used ef-' fectively in such apparatus without the presentinvention.

For. the best utilization er helically finned tubes in fluid heatexchange apparatus there must be a maximum heat transfer per cubic footof space occupied by the apparatus. This. condition requires that, in anapparatus using a bank of hellcally finned tubes, they be overlapped.

directions on,opposite sides ofthe tubes, this action taking placeaccording when used as parts of heat- If adjoining overlappedhelicallyflnned tubes all have their flns arranged as left handhelices.or if all of the tubes have their fins arranged as right hand helices,the tubes cannot be completely interlocked or overlapped'under certain 5conditions. One condition pertains when the pitch is of sufiicientlength, and the fin is of sufilcient length.- In such a situation, the-upward slant of one fln, and-the downward slant of the other wouldcausethe fins of adjoining 10 tubes to contact so as to cause the fins totouch before the fln of one tube touched the adjoin: ing tube. v Amaximum interlocking of adjoining helically finned tubes isnecssary'toobt'ain the maximum amount of heat transfer'surface per cubicfoot of space occupied by the fluid heat exchange apparatus. To permitsuch a maximum of interlocking there must be a limit of pitch for agiven depth of fin.

It is a part of this invention to arrange helically finned tubes in asingle row, the adjacent tubes in a row having helices of-alternatedirectipns. That is to say, the first and third tubes of the row have,for example, flns arranged as right hand helices, and the second andfourth tubes have flns arranged as left hand helices.

A second consideration of the action rtaking place when a stream of gasencounters one of the tubes above mentioned, will now be considered. Thegas passing a tube encounters a fin on both sides of the tube, at anangle to the direction of motion of the stream of gas. The fin then actslike a deflection band. The up,-stream side of the fin actually deflectsthe gas. The gas passing on the down-stream side of the same fin or bandwill not change its direction to follow the fin more than a small angle.If the angle of the fin is sufliciently large, there will be a loss ofcontact between the fin and the gas. This loss of contact causes a partof the down-stream side of the fln to become inefl'ective because it isnot scoured by the gas. In this situation,-the heat transfer is not ascomplete as it is when the fin is at the proper angle. By theexpres'sionflower side of the fln. the downstream side of the-fin ismeant; it is the side opposite the side causing actual de flection of apart of the fluid stream flowing acrossthe tubes. 1

Referringto Fig. 4 of the drawings it will be seen that there is alegend Short circuiting.- This indicates an action taking place at theloweror downstream side of a fin arranged at an Y angle greater than thecritical angle. In the event that action takes place as indicated inFig.

' downward on account of the position of the elements Fig. 4 merely forthe purpose of illustration) due to the fact that the fin is shown atan. angle greater than the critical angle.

It is a part of this invention to limit the helical fins to those of apitch less than the critical pitch. The critical pitch is the greatestpitch at which there is no tendency to short circuit the gas relativeto'the down-stream side of the fin. When the fin has a pitch equal to orless than the critical pitch, there iscomplete contact with the gas.When the pitch of the fin is above the critical pitch there is shortcircuiting on the lower side of the fin. By short circuiting" referenceis made to the loss of gas and fin'contact.

Corresponding to the critical pitch of the helical finther'e is acorresponding critical angle for the boundary face of the fin sectionwhether that section be a part of a. fin or otherwise. The fin might notbe helical in form, but it must comply with the teachings of thisinvention. It must be inclined to the tube surface at less than thecritical angle. The fins may be interrupted, in which case, they will bethe equivalents of vanes. Also the fins may have plane surfaces in whichcase they are inclined, fins. The objective always is to limit the finsso'that the air or gas can contact with the downstream side inspite ofthe inclinations of the fins. r

If the fins of adjoining tubes turn in the same direction, then the gaspassing between those tubes will have a part of its body deflected-inone direction, and an adjoining part of the same gas stream will bedeflected oppositely. For exam- 'ple,one part ofthe gas stream would bedeflected downwardly and an arfioinin'g part of the same streamdeflected upwardly under those conditions. Such action produces eddycurrents, and

causes loss of energy, which energy might otherwise be available forscrubbing the heat transfer surface and promoting efiective heattransfer. In the illustrative arrangement of helically finned tubes heredescribed, the gas stream parts between the helically finned tubes aredeflected in the same direction, and loss of energy is thereby obviated.The downward and upward gas deflections mentioned take place when thetank of finned tubes extends across a gas stream flowing,

horizontally. I This invention which the fiow of an external fluid pastfluid heat exchange tubes is such that the flow is within a rangecapable of economically effecting desirable results in industrialinstallations. This range is referred to as the turbulent "velocitysolid and fluid contact. solid to the direction of fluid flow may be,there range; It is such-that the fluid velocities may cause suchextensive eddy currents that there is a tremendous loss in rate of heatexchange due to loss of contact between the external fluid and the tubescontacted by the fluid. This is accepted terminology, in the science ofaerodynam-' ics, for fluid conditions in which it is a distinct problemto provide for complete fluid and is complete is concerned withapparatus in a contact between the' fluid and the solid. 7

With the illustrative device, there is less eddy current loss of energy.There is an adequately increased proportion of fiow energy used to pro-5 mote heat absorption in the arrangement wherein adjoining tubes havingoppositely directed helices are used. k

The illustrative apparatus minimizes eddy current loss and also'lossesofheat due to ineffective heat transfer by the pitch limitations of thefins whereby all surfaces on both sides of the fin are effective andshort circuits are eliminated. a A maximum amount of heat transfer percubic foot of space occupied by the apparatus 7 is effected by theinterlocking of the fins of adjoining tubes.- This arrangement alsoprovides a more compact apparatus and increases the eifective heattransfer for a given draft loss. 20

In Fig.1 there is shown'a heat exchanger havingfluid conducting tubesliland l2. The tubes ID are indicated as having fins I4 in heat stransfer contact therewith and formed substan- I tially as a continuous.left hand helix about the 25 Fig. 1 includes return bend connectionsl8, connecting adjacent tubes in such manner that the 35 contained fluidflows back and forth across the gas stream, the direction of which isindicated by the arrow 20. Preferably the finned sections of the tubesare mounted in a casing indicated by Y the walls 22 'andjfl. Betweenthese walls there 40 is confined a fluid current.

Securing the fins to the tube by arc,fiame, pressure or resistancewelding brings about good heat transfer relations between the tube andthe fins. Under certain conditions the fins may be brazed or 45solderedto the tubes In Fig. 2, a section of the illustrative tube isshown cut away longitudinally through the tube .and through the fins.There are lines of weld nietal 28 indicated in this figure. The crosssec- 50 tion relationships of the bases of the fins and weld metal isindicated bythe upper part of Fig. 2, wherein deposits 28 and .30 ofweld metal are shown as constituting a broad heat transfer base unitingthe fin to the tube. 55 ,In Fig. 1, the return bends l8 are shown asprovided with flanges 32, preferably held in fluid tight contact withthe flanges 34 on the fluid conducting tubes. 7

.While this invention has been described with 00 reference to particularconstructions it is to be understood that the invention is not limitedthere: to, but that it is of a. scope commensurate with the scope of theappended'claims.

What is claimed is:

1. Fluid heat exchange apparatus comprising,

' in combination, a row of parallel tubes conveying one fluid, means forcausing a second fiuid to move across the rowof tubes, and helicallyar-, ranged external fins on each tube making thermal contact therewith,there being alternate right hand and left hand fins on successivetubesalong the row...

2. Fluid heat exchange apparatus comprising,

in combination, a row of parallel tubes conveying The fluid heatexchahgwapparatus shown in A one fluid, means for causing a second fluidto move across the row of tubes, and helically arranged fins of lessthan the critical pitch on each tube, each flnmaking thermal contactwith its tub"e, there being alternate right hand and left hand fins onsuccessive tubes along the row.

3. In fluid heat exchange apparatus, a bank of parallel tubes throughwhich one fluid moves, means for causing a second fluid to flow acrossthe tubes of the bank, and helical fins in thermal contact with thetubes and alternately arranged on successive tubes as right and lefthand helices, the fins and the tube being completely overlapped orinterlocked so that the fins on one tube are in contact with anadjoining tube.

4. In fluid heat exchange apparatus, a bank of parallel tubes throughwhich one fluid moves, means for causing a second fluid to flow acrossthe bank of tubes, and helical fins in thermal contact with the tubes,and alternately arranged on successive tubes as right and left handhelices, the fins on adjoining tubes being interlocked.

5. Fluid heat exchange apparatus comprising, in combination, a row ofparallel tubes conveying one fluid, means for causing a second fluid tomove across the row of tubes, and helically arranged fins electricallywelded on each tube and making thermal contact therewith, there beingalternate right hand and left hand fins on successive tubes along therow.

6. In fluid heat exchange apparatus, parallel tubes each having helicalflns, the fins on adjoining tubes overlapping and being formedrespectively as right and left hand helices.

and left hand helices.

7. In fluidheat exchange apparatus, parallel tubes each having helicallyextending fins, the fins on adjoining tubes overlapping and being formedrespectively as right and left hand helices,

and wide bases securing the fins to the tubes and 5 acting as a highcapacity heat transfer part.

8. In fluid heat exchange apparatus, parallel tubes each having ahelical fin, the fins on adjoining tubes overlapping and being formedrespectively as right and left hand helices. l0

9. In fluid heat exchange apparatus, a bank of tubes conducting a fluid,and helically arranged fins in thermal contact with the tubes, the finson adjacent tubes being arranged respectively as right and left handhelices. i5

10. In fluid heat exchange apparatus, a plurality of tubes conducting afluid, and helically arranged fins secured on the tubes in thermalcontact therewith, the fins on adjacent tubes being interlocked andarranged respectively as right 20 and left hand helices.

11. In fluid heat exchange apparatus, a plurality of tubes conducting afluid, and helically arranged flns of less than critical pitch inthermal contact with the tubes, the fins on alter- 26 nating tubes beingarranged respectively as'right and left hand helices.

12. In fluid heat exchange apparatus, a plurality of tubes conducting afluid, and helically arranged fins of less than critical pitch in ther-80 mal contact with the tubes, the fins on alternating tubesinterlocking and arranged as right CHARLES E. LUCKE.

